Editing Autonomous building (section)

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[[Image:Nature Loo Waterless Composting Toilet Pedestal.jpg|thumb|right|A composting toilet]]
[[Composting toilet]]s use bacteria to decompose human [[feces]] into useful, odourless, sanitary compost. The process is sanitary because soil bacteria eat the human pathogens as well as most of the mass of the waste. Nevertheless, most health authorities forbid direct use of "[[humanure]]" for growing food.<ref>{{cite book |title= The Humanure Handbook: A Guide to Composting Human Manure|last= Jenkins|first=J.C. |year= 2005|publisher= Joseph Jenkins, Inc.; 3rd edition|location=Grove City, PA |isbn= 978-0-9644258-3-5|pages=255 |url=http://www.humanurehandbook.com |access-date=24 February 2019}}</ref> The risk is microbial and viral contamination, as well as [[heavy metal toxicity]]. In a dry composting toilet, the waste is evaporated or digested to gas (mostly carbon dioxide) and vented, so a toilet produces only a few pounds of compost every six months. To control the odor, modern toilets use a small fan to keep the toilet under negative pressure, and exhaust the gasses to a vent pipe.<ref>See [[composting toilet]] for references.</ref>

Some home sewage treatment systems use biological treatment, usually beds of plants and aquaria, that absorb nutrients and bacteria and convert greywater and sewage to clear water. This odor- and color-free [[reclaimed water]] can be used to flush toilets and water outside plants. When tested, it approaches standards for potable water. In climates that freeze, the plants and aquaria need to be kept in a small greenhouse space. Good systems need about as much care as a large [[aquarium]].

Electric [[incinerating toilet]]s turn excrement into a small amount of ash. They are cool to the touch, have no water and no pipes, and require an air vent in a wall. They are used in remote areas where use of septic tanks is limited, usually to reduce nutrient loads in lakes.

[[NASA]]'s [[bioreactor]] is an extremely advanced biological sewage system. It can turn sewage into air and water through microbial action. NASA plans to use it in the crewed [[Mars]] mission. Another method is NASA's [[urine]]-to-water [[distill]]ation system. A big disadvantage of complex biological sewage treatment systems is that if the house is empty, the sewage system biota may starve to death.